This invention relates to apparatus for the controlled voltage supply of several D.C. drives, especially machine tool drives, in which each drive is connected via a thyristor frequency changer to a three-phase network and a control unit is associated with each frequency changer. The control unit produces firing pulses for the respective thyristors when its drive signal agrees with line-synchronized sawtooth voltages. Voltage supplies of the above-mentioned type are described, for instance, in German Pat. No. 2,524,869 corresponding to U.S. Pat. No. 4,084,223.
Apparatus for the main spindle and feed drives in machine tools are generally installed as separate units in the control cabinet. Each has a control set, which is fed by specially fitted speed and current controllers. In addition, a separate power supply is provided for each unit.
It is an object of the present invention to reduce the cost in a separate voltage supply of the type mentioned above.